Several different methods have been taught in the literature to produce vinylamides. Typically these methods initially involve the formation of precursors which are subsequently pyrolyzed or cracked to yield the desired vinylamides.
U.S. Pat. No. 4,554,377 teaches a method for preparing N-vinylacetamide via the thermal pyrolysis of N-(a-methoxyethyl) acetamide at temperatures of 400.degree. to 500.degree. C., without using a catalyst. A similar method is taught in Japanese Patent Application 60-199685. In this method alkoxyethyl formamide derivatives are produced as precursors which are subsequently subjected to thermal decomposition to form N-vinyl formamide.
U.S. Pat. No. 4.334,097 teaches a process for the synthesis of N-vinyl amides from alkoxyethyl amides and their N-alkyl derivatives by splitting-off alcohols. The starting materials are vaporized and cracked in a furnace with porous silica at temperatures of 225.degree.-300.degree. C. at atmospheric or subatmospheric pressures. U.S. Pat. No. 4,322,271 describes a process in which N-vinyl-N-alkyl carboxylic acid amides are prepared by splitting-off an alcohol from the respective alkoxy precursor with or without a catalyst. The catalysts disclosed are weakly acidic catalysts, such as weakly acidic oxides of Al, Be, Zr and W; weakly acidic phosphates of Ca, Al, Mo, B and W; supported aluminosilicates in the H form., and also ammonium salts. Liquid and gas phase conditions in a temperature range of 60.degree.-350.degree. C. are employed.
U.S. Pat. No. 4,670,591 discloses a process for the preparation of N-a-alkoxyethylformamides, used as precursors to N-vinylformamide. The patent also discloses preparing N-vinylformamide by the pyrolysis of the precursor over catalysts such as SiO.sub.2, alumina, Al.sub.2 O.sub.3, marble, iron, copper, MgO or ZnO. The pyrolysis is carried out at atmospheric or subatmospheric pressure in the temperature range of 300.degree.to 550.degree. C.
U.S. Pat. No. 3.914,304 discloses a process for cracking N-a-alkoxyethyl carboxylic acid amides to form N-vinyl carboxylic acid amides, optionally in the presence of an inert gas such as N.sub.2, Ar or CO.sub.2. Filling bodies made from inert material such as glass, quartz, ceramics, porcelain, carbon, graphite, steel and the like are used to effect heat transfer in the reaction zone. Compressed oxides of zinc, zirconium, thorium, cerium, chromium, magnesium, aluminum and the like are also used. Additionally, U.S. Pat. No. 3,531,471 discloses preparing N-vinyl compounds by heating alkoxyalkyl amides at 50.degree.-200.degree. C. in the gaseous phase over weekly acidic catalysts such as oxides of Al, Be, Zr and W, phosphates of Ca, Al, B and W, and other similar compounds. Similar catalysts and/or processes for cracking alkoxyalkyl amides are disclosed in U.S. Pat. No. 3,377,340 and German patent application 1,165,638.
U.S. Pat. No. 4,578,515 discloses a process for cracking ethylidene bisformamide by heating it to a temperature in the range of from about 150.degree. C. to 750.degree. C., preferably 300.degree. C. to 625.degree. C., for from about 0.1 second to 1 hour in the presence of a solid surface catalyst. The pyrolysis is effected over a non-acidic or weakly acidic catalyst such as glass or marble chips. Other listed catalysts, which largely serve as heat transfer media, include diatomaceous earth, fumed silica, chopped glass fiber, silica gel, formed sand, calcium carbonate and steel. Related disclosures which describe similar pyrolysis technology to produce N-vinylacetamide or N-vinylformamide include U.S. Pat. Nos. 4,490,557 and 4,018,826.